Ubiquinone (coenzyme Q or Q) functions in cells as a redox-active co-enzyme of both mitochondrial and plasma membrane electron transport, as an essential lipid soluble antioxidant, and plays a role in thermogenesis and apoptosis. Dietary Q appears to have beneficial effects in treatment of cardiomyopathies and neuro- and muscle-degenerative diseases. Cells are capable of synthesizing Q, but much remains to be learned about the sites of its synthesis, mechanisms of inter- and intra-cellular transport, and the regulation and enzymology of its biosynthesis. The goals of the proposed research are to characterize the polypeptides of the Q biosynthetic pathway and to define the enzymology of Q biosynthesis. The experimental system takes advantage of eight complementation groups of Q deficient (coq) mutants in the yeast Saccharomyces cerevisiae. The coq mutants provide the basis for the characterization of the Coq polypeptides in both yeast and mammals. Synthetic analogs of Q-intermediates provide reagents that serve both as standards in the isolation and characterization of Q intermediates, and as substrates for in vitro assays of enzyme activities. The intracellular location of the Coq polypeptides will be established, and the interdependence of the Coq polypeptides will be studied in the context of determining whether a multi-subunit complex is required for Q biosynthesis, and where in cells it may function. In vitro assays will be developed to characterize the enzymes in Q biosynthesis, which have been particularly refractory to study, namely the monooxygenase and decarboxylase steps. Human Coq homologs will be tested for their ability to rescue the yeast coq mutants, and Q biosynthesis in bovine and rat heart examined by localization of the Coq polypeptides and enzyme activities. The experimental approach employs a combination of chemistry, genetics and biochemistry to delineate the biosynthetic steps responsible for the production of Q in yeast and mammalian cells.